r1536 is probably faster than 1888 too (specially if you're just comparing default settings superVu vs microVU like ilovejedd pointed out) if even by a little but still doesn't make up for the compatibility upgrades since then, I'd rather keep getting more games working and the stability in the new gui too (thank god for software/hardware mode toggle working almost always now )

Simply said: Use whatever works best for you. I test r1888 against the latest builds occasionally and find it only marginally faster anyway.
On the other hand, r1888 comes with a load of issues I'd rather forget about